Grazing crops

Three things you need to know when grazing crops

Charles Sturt University researcher Shawn McGrath worked on an MLA-funded project to measure how incorporating dual purpose crops (DPC) in the feedbase can impact on sheep production.

Here are three recommendations from the research, which producers planning winter grazing of DPCs need to consider.
1. Serving it up. Given the late start to the season in many areas, producers may be concerned that their crops will not have sufficient dry matter for grazing during the winter, when they need them most. However cereal crops can be grazed at much lower feed on offer (FOO; dry matter/hectare) than pastures. In 2013, we put ewes on the point of lambing onto a wheat crop with FOO of average 330kg DM/ha. By using a moderate stocking rate (10 ewes/ha), crop growth rates exceeded ewe consumption rates and the FOO increased during the crop grazing period. As the ewes had been hand-fed prior to going onto the crop (due to inadequate pasture availability), we continued to give ewes access to some pellets during the transition phase to crop in order to reduce the risk of metabolic diseases.

2. Nutritional needs. When grazing late pregnant and lactating ewes on wheat crops, producers should note that calcium and sodium levels could be below ewe requirements. Magnesium levels could be marginal, and the high potassium and low sodium levels in wheat forage may also reduce magnesium absorption from the rumen. MLA-funded research is underway into the nutritional deficiencies encountered by ewes grazing wheat during late pregnancy (when calcium demand dramatically increases) and lactation (when magnesium demand increases). In earlier experiments we supplied a mineral supplement consisting of magnesium oxide, lime and salt in a 2:2:1 ratio. Ongoing research aims to identify the most effective mineral supplements. Ensuring ewes are in adequate condition score (CS) coming into lambing (CS 3) should assist to maintain ewe health.

3. Canola considerations. Calcium and magnesium levels in canola forage appear to be above ewe requirements, and we have not supplied mineral supplements to ewes grazing canola in our experiments. Fibre levels in canola forage are lower than wheat, however fibre requirements for sheep are not well-defined. Experiments by CSIRO found no benefit in providing roughage to young sheep (in terms of increased growth rates), however we have not supplied additional roughage to sheep in any of our research.

Shawn added that, by reputation, DPCs can accumulate high forage nitrate levels , which can lead to nitrate/nitrite poisoning. Application of nitrogen fertiliser may elevate nitrate levels in plants, so the general industry recommendation has been to avoid pre-grazing applications of nitrogen to minimise the risk of nitrate toxicity in grazing livestock.